VZ52 rifle question

[Anzac15]

Bought this incomplete VZ52 today (no upper hand guard, no mag) as a project. Didn't dawn on me til I got home that the rifle had vent holes over the gas system. Somewhere I heard there was something about this. Most '52's I've seen do not have these. Tried looking it up, the only rifle I found with these vents are the 52/57. Was this just an upgrade?

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